1. Field of the Invention
The present invention relates to a flat panel display and method of fabricating the same and, more particularly, to an organic light-emitting display and method of fabricating the same.
2. Discussion of the Related Art
Generally, organic light-emitting displays (OLED) are emissive displays that emit light by electrically exciting a fluorescent organic compound. OLEDs are considered either active matrix or passive matrix depending upon a mode for driving the pixels, which are arranged in a matrix. The active-matrix OLED has lower power consumption than the passive-matrix OLED, so it is more suitable as a large display having high resolution. OLEDs may be further divided into three types, a top emitting type, a bottom emitting type and a double-side emitting type, according to a propagation direction of light emitted from the organic compound. The top-emitting OLED, unlike the bottom-emitting OLED, is capable of emitting light in a direction opposite to the substrate on which the unit pixels are arranged, and it has a high aperture ratio.
In the top-emitting OLED, a pixel electrode may be formed with a conductive material having excellent reflectivity and a proper work function. However, no single material seems to satisfy these characteristics. Thus, the top-emitting OLED typically employs a multilayer pixel electrode.
FIG. 1 is a cross-sectional view of a conventional active-matrix OLED having a multilayer pixel electrode and method of fabricating the same.
Referring to FIG. 1, a substrate 10 is provided with a display area A and a pad area B. An active layer 20 is formed on the display area A, wherein the active layer has source/drain regions 23 and a channel region 21. A gate insulating layer 25 is formed on the entire surface of the substrate, and a gate electrode 30, corresponding to the channel region 21, is formed on the gate insulating layer 25. Subsequently, an interlayer 35 is formed on the entire surface of the substrate, and source/drain contact holes, which expose the source/drain regions 23, are formed in the interlayer 35.
Next, source/drain electrodes 43 are formed on the interlayer 35, wherein the source/drain electrodes 43 contact the source/drain regions 23 through the source/drain contact holes. Simultaneously, a pad electrode 47 is formed on the interlayer 35 of the pad area B. A planarization layer 50 is formed on the entire surface of the substrate and a via hole 53, which exposes any one of the source/drain electrodes 43, and a pad contact hole 55, which exposes the pad electrode 47, are formed in the planarization layer 50.
Subsequently, an aluminum-neodymium (AlNd) layer and an indium tin oxide (ITO) layer are sequentially deposited and patterned on the planarization layer 50. As a result, a pixel electrode 60, coupled to the source/drain electrode 43 exposed by the via hole 53, is formed on the planarization layer 50 of the display area A, and simultaneously, a terminal pad 65, coupled to the pad electrode 47 through the pad contact hole 55, is formed on the planarization layer 50 of the pad area B. Thus, the pixel electrode 60 and the terminal pad 65 are formed with the AlNd layer 61, 66 and the ITO layer 62, 67. Hence, the AlNd layer 61, as a reflection layer, reflects light emitted from an emission layer thereby forming a top-emitting OLED, which emits light in a direction opposite to the substrate 10.
The terminal pad 65 is bonded with an external module after the OLED is fabricated, and it transmits an electrical signal inputted from the external module. Thus, the terminal pad 65 may be vulnerable to external moisture or oxygen. As set forth above, the terminal pad 65 is formed with the AlNd layer 66 and the ITO layer 67. These layers may be exposed to moisture at the same time, particularly at a lateral surface P of the terminal pad 65. In this case, a galvanic phenomenon may be generated between the AlNd layer 66 and the ITO layer 67. This phenomenon appears when two materials having different electromotive force (EMF) are simultaneously exposed to a corrosive solution. The material having a greater EMF is subjected to corrosion.
Thus, when the terminal pad 65 corrodes, it is possible to decrease its reliability after bonding with the external module. This leads to defects in the OLED, and causes a decrease in yield. A decrease in pad reliability may also be generated when the pad electrode has a single layer structure composed of a material sensitive to external moisture or oxygen.